As the thermoplastic polyester elastomer, thermoplastic polyester elastomers in which a soft segment is a crystallizable polyester including polybutylene terephthalate (PBT), and polybutylene naphthalate (PBN), and a hard segment is polyoxyalkylenes such as polytetramethylene glycol (PTNG) and/or a polyester such as polycaprolactone (PCL), and polybutylene adipate (PBA), have previously been known, and put into practice (e.g. Patent Publications 1, 2).    Patent Publication 1: JP-A No. 10-17657    Patent Publication 2: JP-A No. 2003-192778
However, it is known that a polyester polyether-type elastomer using polyoxyalkylenes in the soft segment is excellent in water resistance and low temperature property, but is inferior in heat aging resistance, and a polyester-polyester type elastomer using a polyester in the soft segment is excellent in heat aging resistance, but is inferior in water resistance and low temperature property.
For the purpose of solving the aforementioned defects, polyester-polycarbonate type elastomers using polycarbonate in the soft segment have been proposed (see e.g. Patent Publications 3 to 8.    Patent Publication 3: JP-B No. 7-39480    Patent Publication 4: JP-A No. 5-295094    Patent Publication 5: JP-A No. 10-231415    Patent Publication 6: JP-A No. 10-182782    Patent Publication 7: JP-A No. 2001-206939    Patent Publication 8: JP-A No. 2001-240663
The aforementioned problems are solved, but the polyester polycarbonate-type thermoplastic polyester elastomers disclosed in these Patent Publications have a problem that the resulting polyester-polycarbonate type thermoplastic polyester elastomer is inferior in retainability of blocking property when the polyester-polycarbonate type elastomer is retained in the molten state (hereinafter, also simply referred to as blocking property retainability in some cases), for the reason of the small molecular weight of polycarbonate diol used as a raw material.
For example, since low blocking property leads to a problem that the melting point of the polyester-polycarbonate type thermoplastic polyester elastomer is lowered, for example, in the case of the joint boots and electric wire covering materials, deficiency of heat resistance becomes a problem in some cases in utility of use under the high temperature environment such as a periphery of an engine of automobiles, in some cases. Patent Publications 4, 7 and 8 disclose rise in the melting point is realized by introducing a naphthalate skeleton as a polyester component, but since introduction of the naphthalate skeleton is expensive, rise in the melting point realized by a polyester component having an inexpensive terephthalate skeleton is desired. In addition, regarding a polyester-polycarbonate type thermoplastic polyester elastomer consisting of a polyester component having a naphthalate skeleton, rise in the melting point corresponding to increase in the cost is demanded.
In addition, in recent years, from a view point of the environmental load and the cost reduction, reutilization of off-specification products, or recycle of commercial goods is demanded. In order to satisfy the demand, high blocking property retainability is required. From the background, development of a polyester-polycarbonate type thermoplastic polyester elastomer having high blocking property and excellent retainability of the blocking property is strongly solicited.
On the other hand, Patent Publications 7 and 8 disclose a process of reacting a polyester component forming a hard segment and a polycarbonate diol component forming a soft segment in the molten state to form a block polymer, and increasing the molecular weight with a chain extender. The process is an effective method as a method of increasing the molecular weight of a block polymer, but since the blocking property and retainability of the blocking property undergo greatly control mainly by a reaction during formation of the block polymer, it is difficult to improve the blocking property and the blocking property retainability by a method of increasing the molecular weight with a chain extender after formation of the block polymer. Therefore, in the prior art, a polyester-polycarbonate type thermoplastic polyester elastomer having preferable property has not been obtained. For this reason, establishment of a process for economically producing a polyester-polycarbonate type thermoplastic polyester elastomer having preferable property is strongly solicited.